Radioactive Decay

Each radioactive isotope will continue to undergo radioactive decay into other isotopes until it is stable (e.g., no longer radioactive). Some isotopes will only need to go through a few decay steps to become stable, while others will go through many radioactive decay steps to become stable. Uranium-238, for example, will undergo 14 radioactive decays to eventually become lead-206 which is stable and no longer radioactive. Some of these radioactive decays will be alpha decays and some of these decays will be beta decays.

As uranium-238 decays into lead-206, it will sometimes decay into a different isotope of its parent uranium isotope and sometimes it will decay into an isotope of a totally different element than its parent. This series of alpha and beta decays is known as the uranium-238 decay series..

Uranium-238 Decay Series

Radioactive Isotope

Half Life

Type of Decay

Uranium-238

4.5 billion years

α

Thorium-234

24 days

β

Protactinium-234

1.2 minutes

β

Uranium-234

245,000 years

α

Thorium-230

75,000 years

α

Radium-226

1,600 years

α

Radon-222

3.8 days

α

Polonium-218

3.1 minutes

α

Lead-214

27 minutes

β

Bismuth-214

20 minutes

β

Polonium-214

0.00016 seconds

α

Lead-210

22 years

β

Bismuth-210

5 days

β

Polonium-210

138 days

α

Lead-206

(stable)

Each radioactive isotope is the parent of the progeny isotope listed below it. Each progeny isotope has a much shorter half-life than uranium-238. This radioactive series will require a little over 6.5 billion years to complete.